Magnetron with variable resonance frequency



April 5, 1960 N. E. BACKMARK 2,931,943

MAGNETRON WITH VARIABLE RESONANCE FREQUENCY Filed Aug. 50, 1955 Fig.2 H 5 Xywen-ron 1 E k iBunKmm' "B31 m'mwm MAGNETRON WITH VARIABLE RESONANCE FREQUENCY Nils Erik Backmark, Enskede, Sweden, assignor to Jakobsbergs Elektrotekniska Fabriker Aktiebolaget, Jakohsherg, Sweden, a joint-stock company of Sweden Application August 30, 1955, Serial No. 531,389

Claims priority, application Sweden September 1, 1954' 6 Claims. (Cl. BIS-39.61)

nited States Patent ing cavity resonators with natural resonance frequencies determined by the dimensions of the segments.

According to one feature of the invention at least one of the end surfaces of the anode in its longitudinal direction is provided with at least one groove protruding into the material of the anode from said end surface, the

groove being arranged such that a recess is obtained in the anode material forming an open connection between adjacent cavities of the cavities in the anode in the anodematerial between the cavities. According to the invention electrically conductive parts or bodies are arranged such as to co-operate with the recesses formed by the aperture between the cavities in the anode in such a manner that the size of the apertures between the cavities, i.e. the metal filling in the apertures between the cavities, is varied when varying the position of said electricallyconductive parts in relation to the anode.

For a magnetron with a ring-shaped anode and radially arranged resonators, the groove forming a recess in the anode material at one ,end surface thereof is arranged concentrically with the anode, the conducting parts co-operating with the recess between adjacent cavities of the anode preferably being arranged on a common support, said support being movable in relation to the anode.

The support for the conducting parts co-operating with said recesses may be either rotatable in which case electrically conductingparts having different dimensions at different locations along the periphery i.e. seen in the rotational direction. of the support are arranged on said rotatable support, the parts having such a shape that, in a certain position of the support inrelation to the ano'de, substantially the same amount of metal filling is obtained in all the apertures between the cavities of the anode. or else the support may be displaceable-in the longitudinal or axial direction of the magnetron body.

With a rotatable support for the conducting parts. said The parts are thus displaceable in a circumferential direction in the groove of the anode body and the dimensions of them are such that the apertures in the anode between the cavities, seen in a radial section through the anode through the walls of the cavities, are varied as the metal parts are moved when rotating the support. Said parts may thus be made in the form of parts insulated from each other and in a number corresponding to the number of cavities or a multiple of it. The conducting parts may also be arranged on a conducting cylindrical shell, which, together with the parts, is arranged in the groove. This shell may then be secured to an insulating support in order to avoid eddy currents when moving the support.

. Preferably the conducting parts arranged movably in v the groove or recesses are, in order to obtain the highest possible frequency variation, designed with such a shape that, at least in some position of the parts in relation to the anode body, they fill out the recesses formed by the groove in the anode walls entirely, seen in 'a radial section through the conducting parts of the anode.

The support for the metal parts protruding into the groove is preferably secured to a shaft arranged concentrically with the mode.

For periodically varying of the resonance frequency of such a magnetron means may be provided for applying to the support and consequently also to the parts protruding into the anode groove an oscillating movement in relation to a desired position of the parts in the anode body or a rotatory motion.

The metal parts arranged in the groove in the anode body may have different shapes as seen in a section perpendicular to the axis of the magnetron, adapted with respect to the desired variation of frequency and with respect to the desired course of the variation of the frequency with time. For different dimensions of the metal parts of the anode in the vicinity of the apertures between the cavities it is convenient experimentally to determine the shape of the movable metal parts which gives the desired variationof the frequency for a continuous rotation or uniformly oscillating movement of the metal parts in the groove.

With a magnetron in which the anode body comprises thin radially arranged plates, forming the cavity walls, a pulse shaped variation of frequency with steep frequency variations may thus conveniently be obtained if the metal parts movable in the groove, in such'a magnetron forming slots in the anode plates have a sharp limitation in tangential direction. By choice of the distances between said metal parts and the size of them in a tangential directionythe time relation between the highest and the lowest resonator frequenciesof thejmagnetron mav be determined. 7 V

By giving the cross section of the metal parts a suitable wave shaped variation in the tangential direction of the cylinder along which the metal parts are arranged a sinesha ed or other Wave shaped v ariation of frequency can be obtained.

In a magnetron device according to the invention, with said movable parts secured to a rotatable supporting body, the frequency of the frequency variation can be made higher than the number of cavities multiplied by the number of revolutionsper second of the rotating support if'the pitch of the .metal parts on the support is made a fraction of the pitch of the cavities, Such a device is particularly advantageous for obtaining'hi h variation frequencies in .magnetrons of the kind earlier referred to providedwith thin plate shaped cavity walls. V In a preferred" embodiment of a magnetronaccording to the invention the driving members for the rotatable support for the metal parts arev arranged entirely within the evacuated vessel of the magnetron. Arrangements and means for this purpose are Well known per se, i.e. from X-ray tube arrangements.

A magnetron device according to the invention may, following the same principles as indicated above, be provided with more than one groove or series of recesses in the anode body described above with displaceable parts arranged in cooperation with the slots formed by said groove in anode body between adjacent cavities of said body.

in an embodiment of a magnetron according to the invention in which the metal parts are displaceable in the grooves or slots described above in the anode body between the cavities in a direction parallel to the axis of the magnetron, said metal parts may together constitute one single tuning ring with the same section along its periphery, the filling of the grooves between the cavities varyingwith the longitudinal displacement of the ring.

A device according to the invention shows considerable advantages in comparison to known embodiments of tunable magnetrons in which a number of rods or radially arranged plates corresponding to the number of cavities are displaceable in the longitudinal direction of the cavity body. Thus in the known devices a minute centering as well as a very exact support in the tangential direction is necessary, while said tuning ring according to the invention only asks for a good centering which can easily be obtained as it is not essential that said tuning ring bears free from the walls of the grooves.

In a device according to the invention with grooves and metal parts arranged as described above frequency variations of about have been obtained with a IZ-cavity anode structure comprising a cylindrical body with radial- 1y disposed vanes of otherwise conventional type and for a wave length of 3 cm.

In the accompanying specification the'principles of the invention will be described with reference to an embodiment of a magnetron according to the invention as appearing from the annexed drawing in which Fig. 1 is a longitudinal sectional view taken through the center of a magnetron made in accordance with the principles of the invention. A

Fig. 2 and Fig. 3 are different embodiments of metal parts, intended to be rotatably arranged in relation to the anode body with the metal parts moving in a groove in said body, forming apertures between the cavities of the anode.

In the device shown in Fig. 1 the anode body 1 is provided with a cylindrical aperture comprising interiorly extending vanes 2, which, together with the anode body 1, form an anode with twelve cavities, having openings in the direction of the circularly cylindrical space 3 within the anode in which the cathode 4 of the magnetron is arranged.

In the embodiment shown, a ring shaped groove is cut in .the anode body such that apertures are obtained between the cavities by means of said groove. Onto a preferably insulating support 6, which may consist of' a circular ceramic disc, conductive teeth 7 are secured. Said teeth'are arranged with such pitch that they all, for a certain position of the support 6, fill up, entirely or in part, the apertures 5 in the vanes between adjacent cavities. Said teeth 7 may beinsulated fromeach other as shown in Fig. 2 or carried by a conducting cylinder 8, V the external diameter of which substantially corresponds to the external diameter of thering shaped groove 5 in theanode.

ins 13 are inserted through an aperture 14 in pole piece it A driving means 15 for the support 6 and teeth 7 is secured to shaft 12 and arranged within the vacuum space of the magnetron as illustrated with the vessel 16 hermetically sealed to the pole piece 9.

In the embodiment shown the groove in the anode structure is arranged such that the apertures between the cavities is located at the parts of the cavities most distant from the centre of the anode structure. With this construction the frequency variations of the device is due substantially to the influence of the teeth on the magnetic lines of force at the bottom of the cavity. Corresponding grooves orapertures may instead or as well be arranged nearer to the centre of the anode structure. A successive transfer from inductive to capacitive action is obtained by successive choice of the location of the apertures -in the cavity walls nearer to centre of the anode structure.

In a device according to the invention with metal parts, for instance in the shape of a ring, displaceable in an axial direction in relation to the anode structure instean of circumferentially displaceable teeth 7, means for applying a vibrational movement back and forth in said axial direction are substituted for the driving means 15.

it is to be understood that the invention is not limited to the embodiment as described above with reference to the drawing which is shown for purposes of illustration only.

I claim: I

1. In an electron discharge device, in combination, an annular anode .unit of electrically conductive material having an inner face forming a substantially cylindrical space within said anode unit; a partition unit composed of a plurality of partition members of electrically conductive material arranged on said inner face of said annular anode unit and extending inwardly into said cylindrical space, said partition members being arranged spaced from each other so as to form resonator cavities between themselves; aperture means in at least one of said above units arranged along a circular line coaxial with said cylindrical space in a plane normal to the axis thereof in such a manner as to connect subsequent resonator cavities with each other; a substantially annular tuning means including conductive elements arranged spaced from the axis of said annular tuning means at the same distance as said aperture means are located from the axis of said cylindrical space; and combined supporting and rotating means arranged coaxially with said cylindrical space within said annular'anode unit and secured to said substantially annular tuning means supporting the same rotatably about its axis coaxial with said cylindrical space and with said conductive elements thereof adapted to rotate along acircular path passing through said aperture means so that upon rotation of said annular tuning means by said rotating means said conductive elements there of will pass throughsaid aperture means and thereby vary the free cross-sectional area thereof 7 whereby the frequency emitted by the device is modulated in accordance with the speed of rotation of said tuning means. V

2. In an electron discharge device, in combination, an annular anode unit of electrically conductive material having an inner face forming a substantially cylindrical space within said anode unit; said anode unit having in said inner face thereof a face portion having a smaller diameter and a portion having a larger diameter; a parti- As alreadydescribed said teeth may be given different shape and size with respect to the desired shape of. the

tion unit composed of a plurality of partition members of electrically conductive'material arranged on said face portion having a smaller diameter and extending inwardly into said cylindrical space, said partition members being arranged spaced from each other so as to form resonator cavities between themselves and extending axially also into that portion of said cylindrical space which is formed bysaid face portion having a larger diameter so as to' form between said partition members and said face portion of larger diameter apertures connecting said resonator cavities with each other, said apertures being arranged substantially along a circular line coaxial with said cylindrical space in a plane normal to the axis thereof; and rotary tuning means including conductive elements arranged spaced from the axis of said rotary tuning means at the same distance as said aperture means are located from the axis of cylindrical space; said rotary tuning means being rotatable about its axis coaxial with said cylindrical space so that by turning said rotary tuning means so as to vary the relative position of said conductive elements and said partition members and thus varying the free cross-sectional area of said aperture means, the device can be tuned.

3. In an electron discharge device, in combination, an annular anode made of electrically conductive material and having an inside wall enclosing a substantially cylindrical space, said anode including a plurality of partition members attached to said wall and each extending radial- 1y towards the axis of said space from said wall with their inner ends equidistant from said axis, and extending axially over part of the axial length of said anode leaving a cylindrical space between the axially facing ends of said partition members and the nearest end face of said anode, so that segmental resonator cavities are formed in said anode between said partition members, said anode being formed with recesses constituting apertures connecting said cavities with each other and with said cylindrical space, said apertures being located along a first circle concentric with said axis; a rotatable tuning means mounted for rotation about said axis within said cylindrical space opposite said partition members and including a carrier member, a plurality of electrically conductive elements projecting from said carrier member towards so that saidfconductive elements are moved across said apertures and through said cavities and thereby vary the free cross-sectional area thereof when said tuning means is turned, a drive shaft attached to said carrier and drive means attached to a portion of said shaft, whereby the frequency emitted by the device in operation is modulated when said tuning means is turned-so as to move said conductive elements into different positions with respect to said apertures.

4. An electron'discharge device as set forth in claim 3, in which said electrically conductive elements of said tuning means have a uniform angular spacing from each other equalling the angular spacing between said partition members.

5. An electron discharge device as set forth in claim 3, in which the number of said electrically conductive elements of said rotatable tuning means is an integerrnultiple of the number of said resonator cavities.

6. An electron discharge device as set forth in claim 3,

including means for adjusting the position of said mov-' able tuning means in axial direction thereof.

References Cited in the file of this patent UNITED STATES PATENTS I 

